Processes for separating and recovering constituents of neutron-irradiated uranium



Nov. 10, 1959 R. E. CONNICK ETAL 2,912,302

PROCESSES FOR SEPARATING AND RECOVERING CONSTITUENTS OF NEUTRON IRRADIATED URANIUM Filed Aug. 21, 1944 4 Sheets-Sheet l 5 TA R T l N G M AT E RIA L SHORT-LIVED F/SS/ON PRODUCTS NEUTRON |RRADIATED Np,Pu,U

LONG-LIVED PISS/0N PRODUCTS U R A N U M INSOLUBLE MATTER STORING U LONG-LIVED F/SS/ON PRODUCTS INSOLUBLE MATTER wmlw ROASTING rye? Pu U F/SS/ON PRODUCTS INSOLUBLE MA TTER T)- DISSOLVING H/VO3 SOLUTION UOg ";Pu ,Pu F/SS/ON PRODUCTS lNSOLUBLE M14 TTER F l LT E RI N G UVSOLUBUE MATTER I DISCARD flsrzmsx os/vorzs SOLUTION gfMfNTgSogu T 0 p r) p (o) 35/0 R C F/SS/ON PRODUCTS TO FURTHER TREATMENT ATTORNEY.

Nov. 10, 1959 R. E. CONNICK ETAI. 2,912,302

PROCESSES FOR SEPARATING AND RECOVERING CONSTITUENTS OF NEUTRON IRRADIATED URANIUM Flled Aug. 21, 1944 4 Sheets-Sheet 4 SOLUTION FROM COLUMBIC OXIDE CARRIER PROCESS V V H 50.. UT/ON F/SS/ON 'PRODUC' 7'5 (M08 7) T' (Noah PRECIPITATING SODIUM URANYL i x EN0 N0 4Iv0 Na Ac ACETATE TO DISCARD I PREC/P/TA TE Na U02 A03 v PU() r/ss/o/v p/eooucrs DISSOLVING IN. (REMINDER) wvo NITRIC ACID OXIDIZING ADDING p (r) HYDROXYLAMMONIUM J CHLORIDE Na Cr 0 PREc/P/m TE c1; 2 0 REC/H714 TE F/SS/ON PRODUC 7'5 Cb 2 0 5 PISS/0N ADDING ADDING PRODUCTS COLUMBIC OXIDE 6,5 0 AND HEATING lN/(OH TO FLOCCULATE COLUMBIC OXIDE SOLN.

SOLUT/ON T0 DISCARD SOLUTION T0 DISCARD 2 0R SALVAGE 2 OR SALVAGE P II I Pu(f) REDUCING p ff) I PRECIPITATING E No N03 SODIUM URANYL W Na Ac ACETATE TO DISCARD I SOLUT/ON OR SALVAGE F .9 4 lL H t f E INXENTOR.

. on)? C END PRODUCT u inj l Kofma n BY George C.P1'men1e[ 2,912,302 Patented Nov. 10, 1959 ice PROCESSES FOR SEPARATHNG AND RECOVERING CONSTITUENTS OF NEUTRON-IRRADIATED URANIUM Robert E. Connick, Berkeley, John W. Goiman, San Francisco, and George C. Pimentel, Berkeley, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Application August 21, 1944, Serial No. 550,436

23 Claims. (Cl. 23--14.5)

The present invention relates to processes of preparing plutonium, and more particularly to processes of separating plutonium from uranium and fission products in neutron-irradiated uranium-containing matter.

It is an object of the invention to provide an improved process of removing impurities or contaminants from plutonium, thereby to produce a useful plutonium product.

Another object of the invention is to provide an improved process of extracting plutonium from a neutronirradiated uranium composition.

Another object of the invention is to provide an improved process of extracting impurities from plutonium and uranium in a neutron-irradiated composition.

A further object of the invention is to provide a process of separating plutonium from uranium and fission products in a neutron-irradiated uranium composition employing columbic oxide as a carrier.

A still further object of the invention is to provide a process of separating plutonium from impurities employing a columbic oxide carrier in conjunction with a sodium uranyl acetate carrier.

Throughout the specification the name plutonium, symbol Pu, is employed to designate the element having atomic number 94. Similarly, the name neptunium, symbol Np, is employed to designate the element having atomic number 93. Thus the symbol Pu or more simply Pu designates the isotope of the element of atomic number 94 having mass number 239; and the symbol Np or more simply Np designates the isotope of the element of atomic number 93 having mass number 239. The elements mentioned are known as transuranic elements (elements whose atomic number are greater than that of uranium), which elements have some chemical properties similar to those of uranium.

The apparent discovery of transuranic elements was first announced by E. Fermi in 1934; at which time Fermi stated that the bombardment of uranium with neutrons gave beta activities which he attributed to transuranic elements of atomic number 93 and possibly greater. From 1934 to 1938 other workers, notably O. Hahn and I. Curie, extended this work, and in 1939 Hahn discovered that the elements which had been believed to be transuranic elements were in fact radioactive madium atomic weight elements produced by the fission of uranium. This discovery of fission by Hahn resulted in great activity by scientists throughout the world, and a great many fission products other than those first identified by Hahn were soon discovered and identified. Such fission products were all of smaller atomic number than uranium, generally of atomic number in the middle of the periodic group, and so far as is known, prior to about June 1940, no positive evidence was found indicating the existence of any transuranic element.

However, in June 1940, E. McMillan and P. Abelson published in The Physical Review, 57, 1185 (1940), their discovery that a 2.3 day activity produced by the bombardment of uranium with neutrons was an isotope of element 93, probably 93 Although McMillan and Abelson surmised that element 94 would be formed by beta decay from element 93 they were unable to produce any positive evidence of its existence, and did not obtain either 93 or 94 in pure form or in macroscopic amounts either as the element or as a compound.

Using the methods of McMillan and Abelson, E. Segre, G. Seaborg and I. Kennedy obtained 93 (Np admixed with other elements and subsequently proved that Np decayed to 94 (Pu and measured the radioactive and fission properties of Pu Then G. Seaborg, J. Kennedy and A. Wahl discovered and developed methods for obtaining macroscopic amounts of Pu free from uranium and other elements.

To aid in the better understanding of the nature of the materials present in irradiated uranium masses, from which plutonium is separated, a description of the reactions which take place by the action of neutrons on the uranium will be given. When natural uranium, either in the form of the metal or its compounds, is bombarded with neutrons, several nuclear reactions take place. Natural uranium consists of a large amount of the isotope 238, about as much of the isotope 235 and about 1746,70) as much of the isotope 234. It has been found that U when bombarded by thermal neutrons, undergoes fission, i.e., a breakdown of its heavy nucleus into two fragments, which, as is generally the case for primary fission fragments, undergo beta-particle disintegration. This is exemplified by the following reaction:

U -l-n-aA-l-B-labout 211 (average) where A represents light fission fragments such as Br, Kr, Rb, Sr, Y, Zr, Cb, Mo, Ma, Ru, and Rh, having atomic masses ranging from 83 to 99 inclusive and atomic numbers from 34 to 45 inclusive; and B represents heavy fission fragments such as Sb, Te, I, Xe, Cs, Ba, La, Ce, Pr, and Nd, having atomic masses ranging from 127 to 141, inclusive and atomic numbers from 51 to 60, inclusive.

Very fast neutrons give observable yields of nuclei with atomic numbers from 45 to 51 and probably small yields of nuclei with atomic numbers smaller than 35 and greater than 60.

In general, the beta-active elements which are initially produced by fission disintegrate, emitting a beta-particle, thereby producing daughter elements with unstable nuclei of atomic numbers increased by one over the parent elements. In turn, the daughter elements similarly disintegrate into elements with unsable nuclei, whereby chains of successive disintegrations occur. The chains are finally terminated by the formation of elements with stable nuclei.

The fission products having a half-life of more than three days remain in the reaction mass in substantial quantities for at least one month after the termination of the reaction, and it is particularly desirable to remove these products. These products are classified into two groups which comprise elements of atomic numbers between 35-45 and between 5160, respectively, and are as follows:

First Group (Atomic Numbers Second Group (Atomic Numbers Atom ie Element Half-Life Atomic Element Halt-Life N o. N o.

55 days. days. 57 days. 32 days. ca. 60 days. 3.2 days. Cb 30 days. 8.0 days. 43 Ma 40 years. 5.4 days. 44 Ru 40 days. 36 years. 44 Ru 330 days. 12.5 day 45 Rh 37 days. 28 days.

340 days. 13.5 days.

That is, U captures a neutron to form U which isotope having a half-life of' 23 minutes disintegrates into Np In turn, Np with a half-life of 2.3 days disintegrates into Pu The Pu formed is relatively stable and only very slowly undergoes alpha-particle disintegration, since it has a half-life of about 2.3' 10 years. The reaction. mass may also contain unreacted uranium, the naturally occurring amounts of UX and UX which: are isotopes of thorium andprotactinium, re-

spectively, and minor amounts of other elements.

To produce plutonium from uranium a mass of uranium is subjected to the action of the neutrons, preferably with neutrons of resonance and thermal energies, to produce a mass containing neptunium and plutonium and fission products. Preferably, the mass is then stored after the termination of the action by neutrons to allow neptunium to decay substantially completely to plutoniunnand at the same time to reduce the amount of radioactive short-life fission products. The irradiated mass is then subjected to treatment, whereby plutonium is separated from other elements present, such as uranium and various fission products.

The separation of plutonium is in general based on the fact that plutonium has two different stable oxidation states in which it has different chemical properties. Thus, for example, plutonium in its lower oxidation or reduced state is insoluble in the presence of fluoride ion in acid solution, while plutonium in its higher oxidation or oxidized state is soluble in the presence of fluoride ion in acid solution. Again, for example, plutonium in its higher oxidation state is precipitated in acid solution by sodium'acetate, while plutonium in its lower oxidation state is not precipitated in acid solution by sodium acetate. Fromthe chemical behavior of plutonium, and from other chemical evidence, it is believed that plutonium in its lower oxidation state is in a +4 oxidation state and occurs in solution as Pu+ ion and that plutonium in its higher oxidation state is in a +6 oxidation state and occurs in solution as PuO ion. Thus, it is felt that the lower and higher oxidation states of the plutonium ions are in the. respective forms Pu+ and PuO similar to the respective forms of the uranium ions; however, these facts have not been conclusively established and, accordingly, plutonium in its lower and higher oxidation states is designated by the symbols Pu and Pu respectively.

It has been found that approximately 1.1 volts are required to oxidize plutonium from its lower oxidation state, Pu" to its higher oxidation state, Pu the value of 1.1.volts being the potential in the system of standard oxidation potentials which is referred to the hydrogen-hydrogen ion couple as zero. The following oxidizing 7 agents are among those which have been found suitable for changing plutonium from its lower oxidation state, Pu to its higher oxidation state, Pu 'peroxydisulfate ion (S in the presence of silver ion-as a catalyst, chlorine, permanganate ion (M110 dichro-V mate ion (Cr o ceric ion (Ce+ and bromate ion' present in the form of uranyl ion and it is desired to separate plutonium from uranium, plutonium must be selectively changed to its lower oxidation state, Pu leaving uranium in its +6 oxidation state. Accordingly, the reducing agent should have either a very slow rate of reducing action on uranyl ion or a sufiiciently low reducing potential so it is unable to reduce uranyl ion. Reducing agents which satisfy this requirement and which have been found to be particularly satisfactory are sulfur dioxide, uranous ion (U hydroxylammonium chloride, hydrogen peroxide and ferrous ion (Fe++).

The difference in the solubility of plutonium in its lower and higher oxidation states, Pu and Pu permits the removal of mixed foreign substances; and previously developed methods for. separating plutonium from neutron-irradiated uranium have been based on this fact.

. Thus, in one process plutonium is selectively reduced to acetate in acid solution. Also, in this process plutonium. is selectively reduced to its lower oxidation state, Pu"

and uranium is precipitated as sodium uranyl acetate and separated from the plutonium which remains in the solution. V

The present process of separating plutonium from foreign substances is based on the discovery that when columbic oxide contacts an acid solution containing plutonium in the lower oxidation state, Pu" it will carry the plutonium leaving various impurities in solution, and that when columbic oxide contacts an acid solution containing plutonium in the higher oxidation state, Pu it will carry certain impurities leaving plutonium in solution. For-purposes of convenience, hereinafter the impurities that are carried by thecolumbic oxide precipitate are referred to as being in a first group, whereas the impuritiesthat are not carried by the columbic oxide precipitate are referred to as being in a second group. A modification of; the present process is based on the further discovery that, in the presence of hydroxylammonium chloride, plutonium in the lower oxidation state, Pu" in acid solution is not carried by columbic oxide. The present process, developed on the basis of these discoveries, has substantial advantages over previous processes. For example, the present process is superior to the fluoride process mentioned above in that operations with highly corrosive acid fluoride solutions are avoided. Likewise, the present process is superior to the sodium acetate process mentioned above in that solutions considerably more concentrated in irradiated uranium can be employed, thereby reducing the volumes of solutions handled. Also, the present process effectively separates certain contaminants whichare not efliciently separated by the sodium acetate, process.

One possible explanation of the action of columbic oxide on plutonium in, acid solution is that plutonium in the lower oxidation state, Pu" is adsorbed by the columbic oxide precipitate, the plutonium firmly adheres to the. surface of the columbic oxide, whereby it is carried with the columbic oxide precipitate. Certain other elements, i.e., some of the'fissiorr products, which are present in-solutionwith plutonium are also carried by the columbic oxide precipitate. For example, columbium, along-life gamma emitter, and. zirconium, a prominent gamma emitter, are produced by fission and are among the fission products carried by the-columbic oxide precipie .In g ner it i o be xpe ed th t the columbic oxide precipitate will tend to carry any element which forms hydroxides or oxides which are insoluble in acid solution.

Accordingly, in the present process the columbic oxide precipitate is employed initially to carry plutonium in the lower oxidation state, Pu away from uranium and certain fission products in solution and subsequently to carry other fission products, such as columbium and zirconium, away from plutonium in the higher oxidation state, Pu in solution. More particularly, to an acid solution containing plutonium in the lower oxidation state, Pu and uranium and certain fission products, there is added a potassium hydroxide solution of columbic oxide, the amount of potassium hydroxide solution of columbic oxide being such that the solution retains its acid character, being more than about 0.001 M in "hydrogen ion, and such that' the gram ion ratio of columbium to plutonium is of the order of 20 or greater.

In the specification the terms plutonium in the higher oxidation state or Pu are intended to designate that oxidation state of plutonium produced by treatment of a plutonium solution with an oxidizing agent from the group including peroxydisulfate ion in the presence of silver ion, chlorine, permanganate ion, dichromate ion, ceric ion, bromate ion and the like as noted hereinbefore. Such oxidation state corresponds to that oxidation state of plutonium characterized by the fact that plutonium remains soluble in acid solutions containing fluoride ion, similarly noted supra. On the other hand, the terms plutonium in the lower oxidation state or Pu when used in the specification, are intended to designate that oxidation state of plutonium produced by treatment of a plutonium solution with a reducing agent from the group including sulfur dioxide, uranous ion, hydrogen peroxide, ferrous ion and the like as noted hereinbefore. Such oxidation state corresponds to that oxidation state of plutonium characterized by the fact that when in acid solution, plutonium precipitates as an insoluble fluoride when contacted by fluoride ion, similarly noted supra.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompartying drawings in which Figure 1 illustrates a portion of the flow diagram of the present process, indicating the preliminary treatment of neutron-irradiated uranium in order to produce a solution of plutonium together with uranium and fission products; Fig. 2 illustrates another portion of the flow diagram of the present process, indicating one embodiment of the initial steps, wherein columbic oxide carrier is employed to separate plutonium from uranium and fission products; Fig. 3 illustrates another portion of the flow diagram of the present process, indicating an alternative embodiment of the initial steps, wherein columbic oxide carrier is employed to separate plutonium from uranium and fission products; and Fig. 4 illustrates a further portion of the flow diagram of the present process, indicating the subsequent steps, wherein sodium uranyl acetate carrier and columbic oxide carrier are employed sequentially to separate plutonium from uranium and fission products.

Referring now to Fig. 1, the reaction mass which is obtained by irradiating natural uranium, either in the form of the metal or a compound, with neutrons is first stored in order to allow most of the neptunium to be converted to plutonium and most of the short-life fission products substantially completely to disappear, due either to beta-particle decay or to isomeric transition. After storage, the mass is roasted at a high temperature, whereby some of the gaseous and volatile fission products, such as krypton, xenon, iodine and bromine are driven off, thereby eliminating the fission products mentioned from the mass. This roasting procedure is not essential and may be omitted, but is advantageous in that the gaseous and volatile fission products mentioned are eliminated from the mass by this preliminary procedure, whereby fewer foreign substances or impurities remain in the mass to be removed by the subsequent and main treatment. The roasted mass is then dissolved in an excess of a suitable acid, such as nitric acid, whereby plutonium is put in solution in both its lower and higher oxidation states, i.e., as Pu" and Pu uranium is put into solution as uranyl ion and various fission products are put into solution. The solution is then filtered, if necessary, to remove any insoluble matter and the volume of the solution is adjusted so that the concentration of uranyl ion in the solution is about 1 to 2 M. The concentration of plutonium normally encountered in this solution will be anywhere from 1.0 10- to 1.0x 10" M depending upon the extent to which the original uranium has been irradiated with neutrons. The solution is then subjected to columbic oxide carrier treatment.

For example, the filtrate prepared in the manner illustrated in Fig. 1 may be subjected to the embodiment of the columbic oxide carrier treatment illustrated in Fig. 2; wherein the plutonium in the filtrate or solution is first selectively reduced. More particularly, in order to make sure that the plutonium in the solution is in its lower oxidation state, Pu" a reducing agent, such as FeSO U(SO or S0 is added to the solution and the solution is agitated for a suitable time interval, about 20 minutes, whereby any plutonium in the higher oxidation state, Pu is positively brought to the lower oxidation state, Pu while uranium remains in solution in the +6 oxidation state as uranyl ion, UO The acidity and sulfate ion content of the solution is adjusted by the addition thereto of appropriate amounts of sodium hydroxide or sulfuric acid and sodium sulfate, such that the HSO; and 50; ions are about 0.1 M and 0.2 M, respectively. The addition at this point of sulfate ion is desirable in that the added sulfate ion subsequently aids in the flocculation of columbic oxide so as to produce a Cb O precipitate which has maximum carrying power.

A potassium hydroxide solution of columbic oxide is then added to the solution mentioned above so that a substantial quantity of Cb O is precipitated in the solution. More specifically, there should be suflicient Cb O precipitated such that the gram ion ratio of columbium to plutonium is of the order of 20 or greater. However, the addition of an excess amount of potassium hydroxide solution of columbic oxide is avoided so that after precipitation the solution still retains its acid character, being more than about 0.001 M in hydrogen ion. Over eighty percent of the plutonium in the lower oxidation state, Pu" is carried out of solution with the columbic oxide precipitate, provided the concentration of uranyl ion in solution is not greater than 1 M. In the event the concentration of uranyl ion is higher than 1 M, a somewhat larger quantity of columbium must be precipitated in order to carry the same percentage of plutonium out of solution. Uranium and fission products, with the exception of fission products comprising elements, the oxides or hydroxides of which are precipitated in acid solution, such as columbium and zirconium, are left in solution. The columbic oxide precipitate carrying plutonium is separated from solution.

The solution is again treated with columbic oxide, but first the acidity of the solution is increased somewhat by the addition of nitric acid. Again a potassium hydroxide solution of columbic oxide is added to the solution mentioned, the amount of potassium hydroxide solution of columbic oxide added being such that the solution retains its acid character, being more than about 0.001 M in hydrogen ion, and such that the gram ion ratio of columbium to plutonium is of the order of 20 or greater. A precipitate of Cb O is produced which carries about eighty percent of the remaining plutonium in the reduced state, Pu out of the solution, approximately the same percentage of plutonium being carried from the lastin a chemical plant.

. +7 mentioned solution as was carried from the first-mentioned solution, as previously explained. The columbic oxide, precipitate carrying plutonium is separated from solution; and, if desired, the last-mentioned solution may be treated a third time with columbic oxide to carry any small amount of plutonium which remains therein.

Ordinarily, in two treatments with columbic oxide, in the manner described, at least about ninety-seven percent oi the plutonium in a solution is carried by the columbic oxide precipitates.

The columbic oxide precipitates produced in the two treatments described above are combined and are then dissolved in 0.1 to 1.0 M'oxalic acid solution. The oxalic acid solution is then somewhat increased in acidity by .the addition of nitric acid. Then an oxidizing agent, such asammonium ceric nitrate, is added to the solution, whereby plutonium is placed in solution in its higher oxidation state, Pu and the oxalic acid is destroyed,

resulting in a partial precipitation of the columbium as Cb O After the oxalic acid'is thus destroyed, sodium hydroxide is added to the solution in order to decrease the acidity thereof, maintaining a hydrogen ion concentration of at least 0.001 M, whereby the remainder of the columbium is precipitated as Cb O The columbic oxide precipitate carries fission products, comprising elements,

the oxides or hydroxides of which are precipitated in acid such as columbium and zirconium, while whereby a solution is obtained containing plutonium which has been separated from uranium and fission products.

In extracting plutonium from neutron-irradiated uranium by the above procedure, it is noted that solutions which are at least 1.0 M, and possibly up to 2.0 M, in uranyl ion may be employed. On the other hand, all other previously developed methods for extracting plutonium from such solutions require that the concentration of uranyl ion in the solutions be much lower and not greater than about 0.25 M in uranyl ion. Thus, employing'thetpresent process large quantities of neutronirradiated uranium may be handled in a given size unit Moreover, in the present process the plutonium is extracted by the columbic oxide precipitate from the solution containing uranium in an initial step, thereby avoiding the necessity of handling large volumes of precipitate, such as is usually the case in pre viously developed processes, such, for example, as the previously mentioned sodium acetate process. Furthermore, the'present process possesses obvious advantages over the previously .rnentioned fluoride process in that corrosion difficulties are avoided. Finally, a desirable feature of the present process resides in the positive removal of radioactive columbium and zirconium by the columbic oxide carrier, whereby each cycle of the process has a very high gamma decontamination efficiency.

Alternatively, the filtrate preparedin the manner illustrated in Fig. 1 may be subjected to the embodiment of the columbic oxide carrier treatment illustrated in Fig. 3. In this embodiment, the filtrate mentioned is treated with an oxidizing agent to bring the plutonium to its higher oxidation state, Pu and then the solution iscontacted with columbic oxide precipitate, whereby plutoniurn is ,left in solution and fission products, such as columbium and zirconium, are carried out of solution; or to the filtrate mentioned there is added hydroxylamzirconium, are carried out of solution, and finally the hy- 'droxylammonium chloride is destroyed. In either case,

subsequently by contacting this solution with a second columbic oxide precipitate V More particularly, in the first case, an oxidizing agent, such assodium dichromate, is added to the nitric acid solution containing uranium as uranyl ion, plutonium, both as PM" and Pu and fission products. The solution is given a heat treatment, whereby it is held at about 75 C. for about one-half hour, being agitated during this interval. Then the solution, after being cooled, is mixed with a potassium hydroxide solution of columbic oxide, whereby columbic oxide precipitate is formed and the solution remains at least 0.001 M in hydrogen ion after the precipitation. I The precipitate is seperated from the solution, whereby gamma-active fission products, co

lurnbium and zirconium, are removed with the precipitate, while uranium, plutonium and fission products remain in the solution. The solution, which contains plutonium in W its higher oxidation state, Pu), 'is now ready for the further steps in the process.

In the second case the hydroxylammonium chloride is added to the nitric acid solution containing uranium as uranyl ion, plutonium both as Pu and Pu and fission products, whereby the plutonium is reduced to its lower oxidation state, Pu The addition of the hydroxylammonium chloride positively prevents plutonium in its lower oxidation state, Pu" from being carried by columbic oxide. Hydroxylammonium chloride is added'in such amount that the NH OH ion concentrationtin the solution is from about 0.03 to 0.10M. Then a potassium hydroxide solution of columbic oxide is added to the solution, whereby columbic oxide precipitate'is formed and the solution is at least 0.001 M in hydrogen ion after the precipitation. The columbic oxide precipitate is separated from the solution, whereby gamma-active fission products, such as columbium and zirconium,are removed with the precipitate, While uraniurn, plutonium and fission products remain in the solution. The solution is then acidified to about 1.0 M with nitric acid and an excess of sodium dichromate sufiicient to destroy the hydroxylammonium and to oxidize the Pu to its higher oxidation state, Pu is added to the solution. The temperature of the solution is then raised to about 75 C. and maintained at that temperature for about one-half hour, being agitated during this interval. This treatment serves to destroy by oxidation the hydroxylammonium ion in the solution and puts the plut. in HNO and then an excess of reducing agent, such as FeSO U(SO or $0 suflicient to reduce the Pu a reducing agent isthereafter added to the solution in order to bring the plutonium to its lower oxidation state,

Pu thereby permitting the plutonium to be removed to Pu is added. 'Thesolution is agitated for a suitable time interval, about 20 minutes, whereby plutonium which is present in the solution in its higher oxidation state, Pu is reduced to its lower oxidation state, Pa

The reduced solution is next adjusted in acidity and sulfate ion content by the addition of sodium hydroxide or sulfuric acid and sodium sulfate, whereby the concentration of HSO4 is about 0.1 M and the concentration of SO is about 0.2 M. Then a potassium hydroxide solution of columbic oxide is added tothe solution, the

amount of potassium hydroxide solution of columbic.

exception of fission products comprising elements, the

oxides or hydroxides of'which are precipitated in acid solutions, such as columbium and zirconium, are left in 9 solution. The columbic oxide precipitate carrying plutonium is separated from the solution.

The solution is again treated with columbic oxide, but first the acidity of the solution is increased somewhat by the addition of nitric acid. Again a potassium hydroxide solution of columbic oxide is added to the solution mentioned, the amount of potassium hydroxide solution of columbic oxide added being such that the solution retains its acid character, being more than about 0.001 M in hydrogen ion, and such that the gram ion ratio of columbium to plutonium is of the order of 20 or greater. A precipitate of Cb O is produced which carries about eighty percent of the remaining plutonium in the lower oxidation state, Pu" out of the solution, approximately the same percentage of plutonium being carried from the solution as was carried by the first Cb O precipitate. The columbic oxide precipitate carrying plutonium is separated from solution; and, if desired, the last-mentioned solution may be treated a third time with columbic oxide to carry any small amount of plutonium which remains therein. Ordinarily, in two treatments with columbic oxide in the manner described at least about ninety-seven percent of the plutonium in a solution is carried by the columbic oxide precipitates.

The columbic oxide precipitates produced in the treatments described above are combined and are then dissolved in 0.1 to 1.0 M oxalic acid solution. To the resulting solution nitric acid is added, whereby the solution is made about 1.0 M in HNO Then an excess of an oxidizing agent, such as ammonium ceric nitrate, is added to the solution in quantity sufficient to oxidize the Pu to Pu and the solution is heated and held at 75 C. for about one-half hour and agitated during the interval, whereby plutonium is placed in its higher oxidation state, Pu in solution and the oxalic acid is destroyed. After the oxalic acid is thus destroyed, resulting in a partial precipitation of the columbium as Cb O sodium hydroxide is added to the solution in order to decrease the acidity thereof, maintaining a hydrogen ion concentration of at least 0.001 M, whereby the remainder of the columbium is precipitated as Cb O The columbic oxide precipitate now carries any traces of fission products, such as columbium and zirconium, the oxides or hydroxides of which are precipitated in acid solution, which were not previously carried from the solution in the first columbic oxide precipitate, as described above; while plutonium being in the higher oxidation state, Pu remains in solution. After the solution is cooled the columbic oxide precipitate carrying fission products, if present, is then separated from solution, whereby a solution is obtained containing plutonium which has been separated from uranium and fission products.

In the present process the embodiment illustrated in Fig. 3 is similar to the embodiment illustrated in Fig. 2 with the exception that in the initial step columbic oxide is precipitated under conditions which cause it to carry fission products, such as radioactive columbium and zirconium, out of the neutron-irradiated uranium solution prior to the extraction of plutonium therefrom. This result is brought about by the treatment of the neutronirradiated uranium solution with columbic oxide when the plutonium in solution is in the higher oxidation state, Pu or when the plutonium is in the lower oxidation state, Pu" and hydroxylammonium chloride is present, thereby preventing the columbic oxide from carrying plutonium, as previously explained. It is believed that this modification or embodiment of the present process as illustrated in Fig. 3 possesses additional advantages over the embodiment of the present process illustrated in Fig. 2 as it has been found desirable to remove certain dangerous gamma-ray emitting fission products, such as columbium and zirconium, initially rather than to concentrate them with plutonium in the first extraction step.

mentioned has a greater gamma decontamination efficiency per cycle than has the initially described columbic oxide carrier process, since in the modified process there are two steps in which the columbic oxide tends to separate plutonium from the gamma-active fission products, columbium and zirconium.

The solution obtained from either embodiment of the columbic oxide carrier process illustrated in Figs. 2 or 3 contains plutonium in its higher oxidation state, Pu which plutonium has been separated from uranium and fission products by the primary separation or decontamination treatment described, employing columbic oxide carrier. This solution usually contains small traces of fission products remaining with the plutonium after the primary separation treatment; and it is generally desirable to remove these small traces of fission products, since even small amounts of such radioactive fission products comprise dangerous and harmful materials. Moreover, some of these fission products are highly absorbent of neutrons and constitute, even in small amounts, highly undesirable impurities in the plutonium. Accordingly, the solution mentioned which has been subjected to primary separation treatment is subjected to secondary separation treatment, whereby the plutonium is further purified or decontaminated.

For example, the solution mentioned may be subjected to secondary purification or decontamination treatment in accordance with the embodiment of the columbic oxide carrier process, illustrated in Fig. 2, the process being repeated exactly as previously specified. The only difierence in this connection will be that the initial solution mentioned contains practically no uranium; thus for this reason the columbic oxide precipitate will carry the plutonium somewhat more efficiently than before. Of course, it will be understood that the secondary purification treatment, employing columbic oxide carrier, as illustrated in Fig. 2, may be repeated one or more times in order to obtain plutonium of the desired degree of purity.

Alternatively, the solution mentioned may be subjected to secondary purification or decontamination treatment, as illustrated in Fig. 4; wherein a sodium uranyl acetate carrier is employed in conjunction with the columbic oxide carrier. More specifically, a solution containing initially purified plutonium in the higher oxidation state, Pu and derived from the embodiment of the columbic oxide carrier process illustrated either in Fig. 2 or Fig. 3 is processed; which solution also contains traces of fission products not previously removed. The solution mentioned is first treated with uranyl nitrate, whereby the solution is made about 0.01 to 0.50 M in uranyl ion. Solid sodium nitrate is then added to the solution in order to make it about 1 to 5 M in sodium ion; and then sufiicient solid sodium acetate is added to the solution in order to precipitate sodium uranyl acetate, the amount of solid sodium acetate added being sufficient so that after the precipitation of sodium uranyl acetate the solution is at least 0.2 M in acetate ion. In the event the initial solution is only slightly acid, a little glacial acetic acid may also be added so that the molar concentration ratio of acetic acid to acetate ion is equal to at least 2.

The sodium uranyl acetate precipitate is then separated from the solution, the sodium uranyl acetate precipitate carrying the plutonium in its higher oxidation state, Pu and minor fractions of certain fission products, such as columbium and zirconium, leaving most of the fission products in the solution. Then the sodium uranyl acetate precipitate is dissolved in an excess of nitric acid; which solution is then subjected to the columbic oxide carrier treatment.

In accordance with a first embodiment of this treatment, a little of an oxidizing agent, such as sodium dichromate, is added to the nitric acid solution of the sodium uranyl acetate, carried plutonium and fission products mentioned in order positively to insure that the plutonium in this solution remains in its higher oxidatated and plutoniumis left in solution as Pu the sodium uranyl acetate precipitate is separated from tion state, P l,1, 9), the concentration of the dichromate ion in. 11.? QlUfibIl'bfiflE 'll-Q a :1 1 9 Potass um hy roxide so utio of c lum i Oxide S a e to th so ution m io ed. f ow n whic the solution 1' is heated to a temperature within the approximate range 70 to ,100 1, whereby columbic oxide is precipitated in a suitable flocculent form. The amount of potassium hydroxide solutionof columbic oxide which is added to the solution mentioned is such that the solution retains its, acid character, beingrnore than about 0.001 M in hydrogen ion. The columbic oxide precipitate calrying "fission-productg such' as columbiu'm and zirconium, is separated from the solution, leaving uranyl ion and plutoniurjnin the higher oxidation state, Pu in the solution[ This solution is then treated with a suitable reducing agent, such as 'hydroxyl-ammonium chloride,

wherebyithe plutonium is .selectively reduced or placed the lower oxidation state, Pu in solution, the uranium remaining in the +6 oxidation state, UO in solution.

In accordance with a second embodiment ofthis treatment, hydroxylammonium chloride is added to the nitric acid solution of sodium uranyl acetate, carried plutonium and fission products mentioned, whereby the plutonium is, reduced to its lower oxidation state, Pu The addition of the"hydroxylanimonium chloride positively preyen ts plutonium in its lower oxidation state, Pu from being carried by columbic oxide. Hydroxylammonium chloride is added in such amount that the NHgOH+ ion concentration in the solution is from about 0.03. to 0.10 M. Then a potassium hydroxide solution of columbic oxide is added to the solution, whereby columbic oxide precipitate is formed and the solution is at least 0.001 M in hydrogen ion after the precipitation. The columbic oxide precipitate carrying fission products, such as coleaving u'ranyl ion and plutonium in the lower oxidation 1 state, Pu" in the solution.

To the solution produced by eitherembodirnent of the columbic oxide carrier treatment described above and containing uranyl ion and plutonium in the lower oxida tion state, Pu there is added sufficient solid sodium nitrate tobring the sodium ion concentration to about 2 to 5 Then an excess of solid sodium acetate is added to the solution'in such quantity that Acion conce'ntration is about 0.2 M, whereby uranium is precipi- Next,

noted. While the previously mentioned sodium uranyl acetate process possesses many advantageous features over other processes, such, for example, as the fluoride process, it alone is not as efiicient asis desirable separating from plutonium certain gamma emitting fission products or contaminants, particularly columbium and zirconium. The above described process of subjecting plutonium to secondary purification illustrated in Fig.

4, wherein sodium uranyl acetate carrier is employed in ,conjunction with columbic oxide carrier, is very advantageous as it overcomes the defect mentioned and pro vides acomposite porcess,wherebysubstantially all of the various'fission products are efficiently removed from the plutonium. Of course, it will be understood that the secondary purification treatment, employing sodium uranyl acetate and columbic oxidecarriers, as illustrated in Fig.

antenna lumbium and zirconium, is separatedfrom the solution,

" from at least some of the other of said constituents 4, maybe repeated one or moretimes in order to obtain plutonium of the desired degree of purity.

Inyiew of the foregoingpit will be understood that after a neutron-irradiated uranium solution has been prepared the rnanner illustrated in Fig, 1, then subjected to primary purification in the manner illustrated Fig. 2 or Fig. 3 and then subjected to secondary purification in the manner illustrated in Fig. .2 or Fig. 4, all in the manner explained, a solution of plutonium is produced-which is substantially completely free of fission products and uranium. This solution containing plutonium may be subjected to a concentrating treatment and combined with other, concentrated plutonium solutions similarly obtained, and then ultimately subjected to suitable chemical treatment, whereby the purified plutonium is obtained as a compound or as a metal. The details of the last-mentioned procedure are not herein described, as such is beyond the province of the present process which pertains primarily to the purification of plutonium and the substantially complete separation of plutonium from uranium and fission products.

It will be understood that the present process is quite flexible and is capable of many modifications. For example, instead of adding a potassium hydroxide solution of columbic oxide to a prepared solution containing plutoniuln in order to efiect the precipitation of Cb O in the prepared solutionQ-a quantity of freshly precipitated Cb o 'produced' externally may be added to the prepared solution. Inthis case, the columbic oxide precipitateis added to the prepared solution and the solution is vigorously stirred in order to insure intimate contact therewith so that it performs the carrying function efiiciently. Moreover, it will be understood v that the columbic oxide precipitate, as well as the sodium uranyl acetateprecipitate, and carried materials are separated from asolution in any suitable manner, such, for example, as by filtration or centrifugation. a c

In the foregoing procedure, aftereach columbic oxide precipitate is separated from solution, it may be washed, if desired. ;A suitable wash solution for this precipitate comprises anaqueous solution which is about 0.01 M in K and 0.001 M in H 50 Similarly, after each sodium uranyl acetate precipitate is separated from solution, it may be washed, if desired. -A suitable wash solu- In view of the foregoing, it is apparent that there has ;been provided; an improved process of separatingplutoniurn' from uraniurnand fission'products in neutronirradiated uranium compositions, -whereby purified plutoniurn, free from contaminants, is obtained, 4 While there has been described what is atjpresent considered to be'thepreferred embodiment of the invention, itlwillibe understood that various modifications maybe" made thereinand it is intended to cover in the appendedclaims all such modifications as fall within the 't'rue spirit'a'nd scope of the invention. a

What is claimed is: I V i 1. In a'pr oces's for recovering plutonium values existing in'the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution in a solution jof the constituents of neutron irradiated uranium, the stepcornprising contacting a columbic oxide precipitate' with said solution to carry plutonium values away whose oxides and hydroxides are soluble in the solution. '2; The process as defined in claim' 1 wherein the steps 9t contacting said solution with columbic oxide precipi tate is conducted while'm'aintaining a hydrogen ion concentration'of atleast 0.001 molar in the solution. "3. The process as defined in claim 1 wherein the amount of columbic oxide precipitate contacted with said solution is; equivalent to a gram ion ratio of colurnbium' to plutonium of at least 20. i

4. The process as defined in claim 1 wherein the step of contacting said solution with columbic oxide is conducted while maintaining a hydrogen ion concentration in the solution of at least 0.001 molar and wherein the amount of columbic oxide precipitate contacted therewith is equivalent to a gram ion ratio of columbium to plutonium of at least 20.

5. The process as defined in claim 1 wherein the columbic oxide precipitate is contacted with said solution in the presence of S and H50; ions of about 0.2 molar and 0.1 molar concentration, respectively, whereby said precipitate is flocculated in the solution.

6. The process as defined in claim 1 wherein said solution has a uranyl ion concentration between 1.0 and 2.0 molar.

7. In a process for recovering plutonium values existing in the'oxidation statewherein plutonium is insoluble in the presence of fluoride ion in acid solution in a solution of the constituents of neutron irradiated uranium, the steps comprising contacting a columbic oxide precipitate with said solution to carry plutonium values away from at least some of the other of said constituents in the solution, and separating the columbic oxide precipitate carrying the plutonium from the solution.

8. In a process for recovering plutonium values existing in the insoluble fluoride oxidation state in an acid solution of constituents of neutron irradiated uranium, the steps comprising treating said solution with a potassium hydroxide solution of columbic oxide to form a columbic oxide precipitate therein which carries the plutonium values away from at least some of the other of said constituents in the solution, and separating the precipitate from the solution.

9. In a process for recovering plutonium values existing in the soluble fluoride oxidation state in an acid solution of constituents of neutron irradiated uranium, the steps comprising contacting a columbic oxide precipitate with said solution to carry those of said constituents whose oxides and hydroxides are insolubleaway from the plutonium values in said solution, and separating the precipitate carrying said constituents from the solution.

10. In a process for recovering plutonium values existing in the soluble fluoride oxidation state in a solution of constituents of neutron irradiated uranium, the steps comprising treating said solution with a potassium hydroxide solution of columbic oxide to carry those of said constituents whose oxides and hydroxides are insoluble away from the plutonium valves in said solution, and separating the precipitate carrying said constituents from the solution.

11. In a process for recovering plutonium values existing in the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution from a solution of the constituents of neutron irradiated uranium comprising a first group of fission product impurities including columbium and zirconium the oxides and hydroxides of which are precipitated in acid solution and a second group including uranium and fission product impurities the oxides and hydroxides of which are soluble in acid solution, the steps comprising treating said solution with a reducing agent selected from the group consisting of sulfur dioxide, uranous ion, hydrogen peroxide, and

' ferrous ion, to reduce the plutonium to the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution, contacting the reduced solution with columbic oxide precipitate, separating the columbic oxide precipitate from the solution, whereby the reduced plutonium and impurities of the first group are carried by the columbic oxide precipitate leaving impurities of the second group in the solution, producing a solution of the plutonium values. and the impurities of the first group carried by the columbic oxide precipitate, oxidizing the solution with an oxidizing agent selected from the group ion, chlorine, permanganate ion, dichromate ion, ceric ion and bromate ion to oxidize the plutonium to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution, contacting the oxidized solu tion with columbic oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby impurities of the first group are carried by the columbic oxide precipitate leaving the oxidized plutonium in the solution.

12. The process of separating plutonium values in the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution from uranium in a +6 oxidation state in a solution comprising selectively reducing the plutonium with a reducing agent selected from the group consisting of sulfur dioxide, uranous ion, hydrogen peroxide and ferrous ion to the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution leaving the uranium in a +6 oxidation state in the solution, contacting the solution with columbic oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby the reduced plutonium is carried by the columbic oxide precipitate leaving uranium in the Pu" oxidation state in the solution.

13. In a process for separating plutonium values in the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution and uranium values in the +6 oxidation state from gamma emitting fission products including columbium and zirconium the oxides and hydroxides of which are insoluble in acid solution, which values and products are in solution, the steps comprising treating the solution with hydroxylammonium chloride, contacting the solution with columbic oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby said fission products are carried by the columbic oxide precipitate leaving plutonium and uranium in the solution.

14. The method of treating a columbic oxide precipitate carrying plutonium in the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution and fission products including the fission products columbium and zirconium whose hydroxides and oxides are insoluble in acid solution comprising dissolving said precipitate in oxalic acid, treating the oxalic acid solution with an oxidizing agent selected from the group consisting of peroxydisulfate ion in the presence of silver ion, chlorine, permanganate ion, dichromate ion, ceric ion, and bromate ion to oxidize said plutonium to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution, reducing the acidity of said oxidized solution to precipitate columbic oxide thereby carrying said fission products from the solution, and separating said precipitate from the solution.

15. In a process for separating plutonium values existing in the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution from fission product impurities including columbium and zirconium whose oxide and hydroxide are insoluble in acid solution, the steps comprising treating the solution with hydroxylammonium chloride, contacting the solution with columbic oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby said impurities are carried by the columbic oxide precipitate leaving plutonium in the solution.

16. The process comprising dissolving columbic oxide precipitate carrying plutonium in the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution and impurities in oxalic acid, treating consisting of peroxydisulfate ion in the presence of silver I the solution with nitric acid and ammonium ceric nitrate in order to oxidize the plutonium to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution and to precipitate columbium as columbic oxide, and then separating the columbic oxide precipitate from the solution, whereby impurities including the fission products columbium and zirconium are carried by the columbic oxide precipitate leaving the oxidized plutonium in the solution.

17. The process of separating plutonium values from uranium and fission products in a neutron-irradiated uranium composition comprising producing a solution of the composition, in which the uranium is in the +6 oxi- ,.dation state'and at least some of the plutonium is in the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution, oxidation states, respectfully selectively reducing the plutonium to the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution with a re- .ducing agent selected from the group consisting of bium and zirconium whose oxides and hydroxides are insolublein acid solution are carried by the columbic oxide i precipitate leaving uranium in a +6 oxidation state and other fission products whose oxides and hydroxides are soluble'in said solution, dissolving the columbic oxide precipitate carrying plutonium and the first group of fission products in oxalic acid, treating the solution with an oxidizing agent selected from the group consisting of peroxydisulfate ion inthe presence of silver ion, chlorine, permanganate ion; dichromate ion, ceric ion, and bromate ion, in order to oxidize the plutonium to theoxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution and to precipitate columbium as columbic oxide, and then separating the columbic loxide precipitate from the solution, whereby fission products of said first group are carried by the columbic oxide precipitate leaving plutonium in the solution.

plutonium is insoluble in the presence of fluoride ion in "acid solution, treating the solution with sodium dichromate to oxidize the plutonium to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution contacting the oxidized solution with columbic oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby fission products are carried by the columbic oxide precipi tate leaving plutonium and uranium values in the solution.

and bromate ion in order to oxidize the plutonium to the oxidation state wherein plutonium is soluble inthe presence of fluoride ion in acid solution, contacting the solution with a columbic oxide precipitate, separating the columbic oxide precipitate from the solution, whereby fission products including columbium and zirconium whose oxides and hydroxides are insoluble in acid solureducing the plutonium in the solution" with a reducing agent selected from the group consistingof sulfur dioxide, uranous ion, hydrogen peroxide, and ferrous ion, contacting the solution with columbic" oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby the reduced plutonium is carried by the columbic oxide precipitate leavingpranium in a +6 oxidation state in the solution.

20. The process of separating plutonium values from uranium and fission products in a neutron-irradiated 'uranium'composition" comprising producing a solution of the composition, in which the uranium is in a +6 oxidation state and at least some of the plutonium is in the oxidation state wherein plutonium is insoluble in the presence of fluoride ion in acid solution, treating the solution with an oxidizing agent selected from the group consisting of peroxydisulfate ion in the presence of silver ion, chlorine, permanganate ion, dichromate ion, ceric ion, and bromate ion in order to oxidize the plutonium in the v solution to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution contacting the'oxidized solution with columbic oxide precipitate, separating the columbic oxide precipitate from the solution, whereby fissionproducts are carried by the columbic oxide precipitate leaving plutonium and uranium in the solution, selectively reducing the plutonium in the solution to the oxidation state wherein plutonium is insoluble'in the presence of fluoride ion in acid solution with a reducing agent'selected from the group consisting of sulfur dioxide, uranous ion, hydrogen peroxide and ferrous ion, contacting the solution with columbic oxide precipitate, separating the columbic oxide precipitate from the solution, whereby the reduced plutonium is carried by the columbic oxide precipitate leaving uranium in a +6 oxidation state in the solution, dissolving the columbic oxide precipitate carrying the reduced plutonium in oxalic acid, treating the solution with an oxidizing agent selected from the group consisting of peroxydisulfate ion in the presence of silver ion, chlorine, permanganate ion, dichromate ion, ceric ion, and bromate ion in order to oxidize the plutonium to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution and to precipitate columbium as columbic oxide, and then separating the columbic oxide precipitate from the solution, whereby the oxidized plu- 'tonium is left in the solution.

cluding columbium and zirconium values from plutonium and, uranium in a neutron-irradiated uranium composition comprising dissolving the composition innitric acid,

. whereby the uranium and the plutonium and fission product values including columbium and zirconium values are the columbic oxide precipitate leaving plutonium and uranium ionic values in the solution. a

22 The process of separating plutonium values from uranium and fission products in a neutron-irradiated uranium composition comprising producing a solution of the composition, in which the uranium is in a +6 oxidation state, treating the solution with hydroxylammonium chloride, contacting the solution with columbic oxide pre cipitate, separating the columbic oxide precipitatefrom ,the solution, whereby fission products are carried by the tion are carried by the columbic oxide precipitate leaving 7 plutonium and uranium values in the solution, selectively values in the .solution, destroying the hydroxylammonium "chloride, selectively reducing the plutonium in the solution with a reducing agent selected from the group consistingof sulfur dioxide, uranous ion, hydrogen peroxide,

and ferrous ion to the oxidation state wherein plutonium is'insoluble in the presence of fluoride ion in acid solution, contacting the solution with columbic oxide precipi- -tjate, separating the columbic oxide precipitate fromthe 'solution, whereby the reduced plutonium'is'carried by the columbic oxide precipitate leaving uranium in a +6 oxidation'state in the solution, dissolving the columbic oxide precipitate carrying the reduced plutonium in oxalic acid, treating the solution with an oxidizing agent selected from the group consisting of peroxydisulfate ion inthe presence of sllver ions, chlorine, permanganate, di-

21. The process of separating fission product values in- 17 chromate ion, ceric ion and bromate ion in order to oxidize the plutonium to the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution and to precipitate columbium as columbic oxide, and then separating the columbic oxide precipitate from the solution, whereby the oxidized plutonium is left in the solution.

23. The process of separating plutonium values from uranium and fission products in a neutron-irradiated uranium composition comprising producing a solution of the composition, subjecting the solution to primary treatment, whereby the uranium and a majority of the fission products are separated from the plutonium and a minority of the fission products, treating the plutonium and associated fission products to produce a solution in which the plutonium is in the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution, contacting the solution with sodium uranyl acetate precipitate, separating the sodium uranyl acetate precipitate from the solution, whereby plutonium and traces of fission products are carried by the sodium uranyl acetate precipitate leaving most of the minority of the fission products in the solution, producing an acid solution of the sodium uranyl acetate precipitate in which the plutonium is in the oxidation state wherein plutonium is soluble in the presence of fluoride ion in acid solution, contacting the solution with columbic oxide precipitate, and then separating the columbic oxide precipitate from the solution, whereby the traces of fission products are carried by the columbic oxide precipitate leaving plutonium ionic values in the solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,120,551 Sehwerin Dec. 8, 1914 2,544,476 Werner May 22, 1951 2,577,097 Werner Dec. 4, 1951 2,766,185 Fries et a1. Jan. 1, 1957 2,785,951 Thompson et al Mar. 19, 1957 OTHER REFERENCES 

1. IN A PROCESS FOR RECOVERING PLUTONIUM VALUES EXISTING IN THE OXIDATION STATE WHEREIN PLUTONIUM IS INSOLUBLE IN THE PRESENCE OF FLUORIDE ION IN ACID SOLUTION IN A SOLUTION OF THE CONTITUENTS OF NEUTRON IRADIATED URANIUM, THE STEP COMPRISING CONTACTING A COLUMBIC OXIDE PRECIPITATE WITH SAID SOLUTION TO CARRY PLUTONIUM VALUES AWAY FROM AT LEAST SOME OF THE OTHER OF SAID CONSTITUENTS WHOSE OXIDES AND HYDROXIDES ARE SOLUBLE IN THE SOLUTION. 